In an image-reading device which reads image data of a manuscript so as to provide data for various types of processing, such as in a copier or scanner, light from a light source such as a fluorescent lamp is illuminated onto the manuscript, and the light reflected from the manuscript is made to be incident onto a light receiver equipped with a photoelectric conversion device, such as a CCD. In a still-manuscript-type image-reading device, such as the image-reading device described in Japanese Laid-Open Patent Application H10-257252, the light of the light source is illuminated onto a manuscript placed on a platen glass and remains still while the light source moves. Because the optical path length from the manuscript to the light receiver must remain constant even if the illuminating position with respect to the manuscript changes, mirrors for directing the reflected light to the light receiver, etc., are moved with the light source along the manuscript.
A full-rate carriage and a half-rate carriage, that are movably positioned within a box-shaped frame that supports the platen glass at the top of the frame, are used to move the light source lamp and the mirrors. The full-rate carriage carries the light source and is moved over the entire area of the manuscript. It is equipped with a first mirror for directing the reflected light to the half-rate carriage. The half-rate carriage is moved half the distance that the full-rate carriage is moved, and is equipped with second and third mirrors for directing the light reflected by the first mirror to the light receiver.
When the image-reading device is transported to a different location, the full-rate carriage and the half-rate carriage can easily be moved by dynamic forces. To prevent this during a move, the full-rate carriage and the half-rate carriage are each fixed to one wall of the box-shaped frame using a carriage fixing screw that passes through the wall and secures the carriages at a fixed position along a wall of the box-shaped frame. After the image-reading device has been positioned at its new location, the carriage fixing screw is removed in order to allow the full-rate carriage and half-rate carriage to operate.
A carriage fixing structure of an image-reading device is described in Japanese Laid-Open Patent Application 2001-197259. In the carriage fixing structure of this image-reading device, a fixing screw for preventing a retaining ring from coming off is provided at the base of the box-shaped frame that supports the platen glass, and female threads that receive the fixing screw are formed in the carriage. The tip of the fixing screw is formed into a part of a sphere, and the female threads are formed at the peak of a truncated conical recess formed at the base of the carriage. Thus, the fixing screw can be guided into the recess and easily screwed into the female threads. However, the fixing screw is provided at the base of the box-shaped frame and a space for arranging the fixing screw below the box-shaped frame is needed, and this hinders making the image-reading device thin. Accordingly, it is desirable to operate the fixing screw from the side of box-shaped frame.
Recently, higher image-quality and a faithful reproducibility have come to be required for image-reading devices of this type. For example, in the case of producing a replica by a copier or in the case of reproducing a manuscript on a display connected to a personal computer, it is necessary to obtain image data more precisely.
In order to prevent dust from adversely affecting the detected image, the box-shaped frame that supports the platen glass can be sealed so as to be dust-proof. However, as mentioned above, since the carriage fixing screw is removed after the image-reading device is positioned in a new location, the through-hole for passing through the screw remains in the wall. Therefore, dust from the through-hole can invade the box-shaped frame and adversely affect the performance of the image-reading device.